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The present invention generally relates to measuring the amount of lateral or axial force exerted on tires and more particularly to directly measuring such axial force in order to determine the grip performance of the car.
A variety of techniques have been proposed to measure the performance of vehicle, e.g., an automobile, a motorcycle, etc. One important parameter of vehicle performance is that of xe2x80x9cgripxe2x80x9d. Grip is defined as the ability of a vehicle to maintain contact with the road surface during operation and is of particular importance when the vehicle is cornering. If the desired grip force exceeds the resistance afforded by the road surface, the tire will slide resulting in the vehicle deviating from its driver intended path. Such deviation can range from a nominal slippage of the car to triggering a catastrophic roll over with a variety of intermediate conditions ranging from spins to power slides.
Advantageous proposals aimed at measuring the grip performance of a vehicle (or more accurately, the grip performance of the tires of a vehicle) include U.S. Pat. Nos. 5,435,193 and 5,821,434. These proposals isolate the uprights from the axle and associate a force sensing system therebetween. The force sensing system now can experience the loads placed on the tires without interfering with the operation of the vehicle""s suspension system. A processor can resolve the measuring loads into an axial and a radial component with the axial component being desired for grip performance analysis. Such system functions whether the vehicle is traveling in a straight line or around corners at low speed or at high speed. This system is especially useful in racing contexts.
Other proposals include Miyazaki (U.S. Pat. No. 5,186,042) who proposes a device for measuring the action force of a wheel, which device comprises a stress detection sensor mounted in a hole provided in a vehicle axle, and a signal processing circuit to process a detection signal from the stress detection sensor. Miyazaki teaches that as the stress detection sensor is embedded in the axle, interferences to the sensor output signal from wheel action forces other than the xe2x80x9ctargetxe2x80x9d wheel action force may be decreased.
Goldberg (U.S. Pat. No. 4,371,191) proposes to adjust an automobile suspension system that is responsive to sensed attitude and force changes to change the wheel camber in order to optimize tire contact with the road surface. Goldberg contemplates a system that monitors the forces acting on the vehicle, the direction and degree that the steering wheel is tuned, the relative height of each wheel to the vehicle body, the rotational speed of each wheel, and the camber of each wheel with respect to the vehicle body. A processor coordinates any sensed variations in the vehicle due to changes in the monitored variables, and, in turn, sends out signals to cause an adjustment to be made in the wheel effected.
DE 34 09 040.1 is designed only to determine the lateral force exerted on a wheel (or tire) of a vehicle. Such measurement is achieved while the vehicle is traversing a straight track. Forces due to curves, sloping roadways, wind, and the like, should be subtracted from the simple lateral force exerted by the wheel on the vehicle chassis according to this patent.
Lacking in these proposals is the ability to directly measure only the axial forces exerted on vehicle tires without having to resolve complex forces into component vectors, whether the vehicle is traveling slow, fast, in a straight line, around corners, on flat roadways, or on hilly roadways. It is to such a system that the present invention is directed.
The present invention is an alternative implementation of the load isolation technology disclosed in U.S. Pat. Nos. 5,435,193 and 5,821,434. To that end, the axial or grip force between at least one wheel of a vehicle and a ground surface, wherein the wheel is mounted on an upright and carried by an axle, is directly measured. The axle is radially supported in the upright by roller bearings. The lateral load is supported by the use of thrust bearings. Disposed between the axle lateral thrust bearing assembly and the upright is a force sensor. The force sensor directly registers axial force on the axle with respect to the upright, which is attached to the vehicle chassis. Axial (or lateral) output force signals from the force sensor can be sent directly to a readout device or can be sent to a processor, for example, for treatment. Such a design results in isolating the lateral or axial force vector placed on the axle, which carries the wheel and tire assembly, and, thus, the directly measuring the grip force of the tire.
Advantages of the present invention include the ability to reduce the inside diameter area of upright assemblies and increase available airflow through the upright in some vehicle designs. Another advantage is the potential weight reduction (about 2-3 pounds per axle) of the inventive system compared to prior grip force measurement systems because of the smaller radial load carrying bearings used in the inventive system. A further advantage is that xe2x80x9cgripxe2x80x9d force is measured with a single load cell output by introduction of a roller bearing assembly, which allows axial mechanical freedom. These and other advantages will be readily apparent based upon the disclosure set forth herein.